ENIAC Definition

ENIAC, short for Electronic Numerical Integrator And Computer, was the world's first fully electronic1, general purpose, programmable computer.

It was built by J. Presper Eckert and John V. Mauchly, who began work on it in May 1943 at the Moore School of Electrical Engineering at the University of Pennsylvania. Designated project PX, it was funded by the Army Ordnance Department, which wanted a more efficient way to calculate ballistics tables for artillery during World War II2. The machine was completed in 1945, and it was then used extensively for a variety of purposes for a decade.

ENIAC was preceded in 1941 by the German Z3, which was the first general purpose, programmable electro-mechanical computer. It was also preceded by the Colossus, which was built in 1944 in the UK and which was all electronic and reprogrammable by rewiring but was not general purpose (it was used only for code breaking). The IBM ASCC (Automatic Sequence Controlled Calculator), delivered to Harvard University in the same year, was the first large-scale automatic digital computer in the U.S. Whereas the Z3 and ASCC used electro-mechanical relays in their arithmetic operations, the Colossus and ENIAC utilized vacuum tubes.

Despite its pioneering role, in some respects ENIAC was not the most advanced computer at the time of its development and completion. In particular, unlike the Z3 and ASCC, it initially had to be rewired in order to run a different program; however, this requirement was replaced in 1948 by the use of an array of switches. Moreover, in contrast to the Z3 and virtually all modern computers, ENIAC used decimal arithmetic rather than the binary system (as its developers believed that this could reduce the number of vacuum tubes required, and thereby increase reliability and reduce cost).

ENIAC was completed too late to be used for wartime ballistics calculations. Instead, its first real task during test operations in November 1945 was calculations for studies of nuclear chain reactions for development of the hydrogen bomb. It became formally operational in February 1946, but it was then turned off in November of the same year for refurbishing and a memory upgrade. In 1947 it was transferred to the Aberdeen Proving Grounds in Maryland, where it was turned on in July and remained in continuous operation until its last days.

ENIAC stored digits in ten-position ring counters. Arithmetic was performed by counting pulses with the ring counters and generating carry pulses if the counter wrapped around, in order to electronically emulate the operation of the digit wheels used in mechanical adding machines. Each of the twenty 10-digit signed accumulators could perform 5,000 simple addition operations per second, and a total of 357 multiplication operations or 38 division or square root operations could be performed per second.

ENIAC received a great deal of publicity, in large part because of its huge size. It measured approximately 2.4m by 0.9m by 30.5m and weighed roughly 30 metric tons. It contained 17,468 vacuum tubes, 7,200 crystal diodes, 1,500 relays, 70,000 resistors, 10,000 capacitors and close to five million hand-soldered joints. All of this consumed about 160 kW of power. Today, an equivalent computing power could be easily accommodated on a chip of silicon scarcely larger than a coarse grain of sand. The total cost was nearly $500,000.

Data was fed into the computer via punched cards, the setting of switches on external panels and the connection of cables. The main memory consisted of punched cards, which made it basically infinite. However this was not only extremely slow, but also it required the careful attention of an operator to transfer cards from a punching unit to the card reader unit.

Among the many other major differences from modern computers is the fact that ENIAC ran programs directly and without the use of any operating system. In fact, the concept of operating systems had not even been invented.

Some electronics experts were convinced that ENIAC would not be practical because of the high frequency of vacuum tube failures due to the relatively poor reliability of the tubes that were available at the time. The high burnout rate (on average several tubes per day) did turn out to be a major problem, resulting in the computer being nonfunctional about half the time. However, as most of these failures occurred during the warm up and cool down periods, when the tubes were under the greatest thermal stress, it was soon realized that the solution was to keep the computer running continuously, thereby reducing the number of tube failures to only about one every two days.

ENIAC retained its role as the world's main computer through 1952 because of its unsurpassed ability to solve problems that involved large numbers of arithmetic operations. During its more than 80,000 hours of operation, in addition to ballistics calculations, it facilitated important advances in a number of engineering and scientific fields, including cosmic rays, nuclear energy and weapons, random numbers, weather prediction and wind tunnel design.

Although improvements continued to be added to increase its speed and reliability, ENIAC could not compete with the faster and more economical machines that became available beginning in 1953. Thus its work load was gradually shifted to them, and its power supply was finally turned off on October 2, 1955.

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1In this context, fully electronic refers to the fact that the internal calculations were performed entirely electronically and without making use of mechanical parts or electromechanical relays. However, ENIAC was not fully electronic in the broader sense that manual rewiring (in the form or removing and inserting cables from and into sockets) was initially necessary for reprogramming and input and output made use of punched paper tape and punched cards.

2This was of great importance to the war effort. Advances in weaponry made it possible to reach targets at greater distances and with more explosive power, but such increased distances and other factors made it more necessary than ever to have precise data about angles for the positioning the guns in order to achieve accuracy of the shooting. Tables of ballistics data were laboriously created by humans, whose professional title was computer (i.e., one who computes), who spent all day carrying out the calculations on paper.